Problem: 5 markers cost $7.55. Which equation would help determine the cost of 4 markers?
Solution: There are several equations that could help determine the cost, each with a slightly different approach. We know the cost of 5 markers. We want to know the cost of 4 markers. We can write the numbers of markers as a proportion: $\dfrac{5}{4}$ We know 5 markers costs $7.55. We can let $x$ represent the unknown cost of 4 markers. The proportion of these costs can be expressed as: $\dfrac{\$7.55}{x}$ The cost changes along with the number of markers purchased, and so the two proportions are equivalent. $\dfrac{5}{4} = \dfrac{\$7.55}{x}$